The present invention relates generally to an improved endless flexible abrasive belt, and more particularly to an improved means for splicing the belt along a butt joint formed in the structure. The splicing system has been found to be extremely durable, and resistant to both tensile and peel failure. For most of the materials employed as backing sheets for abrasive belts, it has been found that the splicing system of the present invention provides a cohesive strength which exceeds that of the backing sheet, thus providing a system wherein belt failures normally occur in areas other than in the splice.
In abrasive belts, butt splices are preferred in order to permit the endless belt to be driven in either axial direction. Butt splices typically have been made utilizing strips of a woven backing sheet having a parallelogram form, wherein the splice is formed along a bias direction. Typically, the edges of the backing material are abutted together, and thereafter joined together with a reinforcing strip which is bonded to the underside of the abrasive belt. Typically, the butt joints which have been utilized for flexible abrasive belts in the past have possessed substantial thickness dimensions, thereby forming a belt having a thickness which is greater at the splice than elsewhere.
Another technique which has been employed to form an endless flexible abrasive belt has been to form a tube of woven fabric by sewing a seam across a double thickness of the fabric. This technique presents problems in that the sewn seam creates a material build-up which adds significant thickness to the belt, thereby adversely affecting accuracy during abrasive machining or abrasive planing of various workpieces. Furthermore, in a joint of this kind, the abrasive belt had a requisite machine direction for usage, this tending to detract from the versatility, utility, and ultimate value of the product.
For many operations where uniformity is desired, and wherein bumping or thumping of the belt is deemed undesirable, any increased thickness in the area of the splice is a definite disadvantage, since the degree of accuracy available in an abrasive grinding or abrasive planing operation may be significantly reduced, and furthermore the durability of the abrasive belt will be adversely affected.
In preparing the splicing material for use in connection with the present invention, it is desired that a multiplicity of fibers be provided which span the butt joint present in the belt. These fibers are disposed generally parallel, one to another, and are oriented generally parallel to the central axis of the abrasive belt. Furthermore, the fibers are free of transverse fibers, thereby improving or otherwise enhancing the strength of the splice, without adversely affecting or unnecessarily increasing the thickness. In this connection, therefore, the fibers used to provide reinforcement in the splice extend generally in the machine direction, that is, generally along or parallel to the axis of the belt. The splicing material is preferably pre-formed in order that the angular bias present in the splicing material will be substantially the same as that used for the angular bias of the ends of the parallelogram used to form the endless belt. It will be appreciated, of course, that the reinforcing fibers need not be arranged along an axis which is precisely parallel to that of the abrasive belt, it being appreciated that certain axial deviations may be utilized with good results.
While adhesive tapes have been employed in the past for the preparation of butt-splices in abrasive belts, these tapes have normally employed a woven fabric having both machine direction and transverse direction fibers. In other words, the fibers are normally present in the splice in both axial and transverse directions. In other applications, randomly oriented fibers have been employed to form the fabric portion of the splicing material. Both of these techniques suffer from the disadvantage of having the thickness of the belt increased to an undesirable extent, particularly in the area of the splice.
In accordance with one aspect of the present invention, it has been found that long lengths of usable tape may be prepared for replacing the sewn seam or multi-directional fibers reinforcements used in the past. The tape is prepared by laminating reinforcing fibers along a certain orientation to an adhesive material, and thereafter forming a spirally wound tube with a preferred angular bias for the fibers. As an alternate preparation technique, the tape material may be wound on a straight tube and thereafter bias-slit so as to form the tape material having the fibers arranged in an appropriate angular bias. For convenience in use and application, a film or foil may be used as a backing member to assist in processing, with the film or foil being optionally removed following completion of the formation of the splice.
In order to still further reduce the extent to which the belt thickness is increased in the area of the splice, the edges of the area in the belt forming the splice are preferably relieved in order to permit the splicing material to be inset. This removal of material, when undertaken, can be accomplished by any suitable means such as grinding or the like, and is done in order to permit the splicing material to be positioned along the belt without adversely affecting the thickness by adding significant dimensions to the belt in the area of the splice. In certain instances, however, removal of material is not essential.
Therefore, it is a primary object of the present invention to provide an improved splicing system for an abrasive belt, wherein a multiplicity of reinforcing fibers are laminated or otherwise retained within an adhesive member to be secured to the areas of the belt adjacent the butt splice, and wherein the axis of the individual fibers are arranged generally parallel one to another, and preferably along an axial direction which is generally parallel to the machine axis of the belt.
It is a further object of the present invention to provide an improved splicing system to prepare butt splices in endless abrasive belts, and wherein the splice is formed with an adhesive bond spanning the joint, and with a multiplicity of unidirectionally disposed fibers being present to reinforce the adhesive film, the fibers having an exceptionally high modulus and high tensile strength.
It is yet a further object of the present invention to provide an improved splicing system for abrasive belts, particularly for the preparation of butt joints in abrasive belts wherein the joint may be prepared without adversely affecting the thickness of the belt in the area of the splice.
Other and further objects of the present invention will become apparent to those skilled in the art upon a study of the following specification, appended claims, and accompanying drawing.